SRL Proxemics: Spatial Guidelines for Supernumerary Robotic Limbs in Near-Body Interactions

Paper Title

SRL Proxemics: Spatial Guidelines for Supernumerary Robotic Limbs in Near-Body Interactions

Publication Info

• Topic area: Human-robot interaction with wearable supernumerary robotic limbs (SRLs) in near-body contexts.
• Keywords: Supernumerary robotic limbs, proxemics, human-robot interaction, perceived safety, trust, autonomy, embodiment, spatial interaction, wearable robotics.

Background and Problem

• Problem / challenge: Existing SRL systems lack a systematic framework for managing spatial behavior and autonomy in near-body interactions. Current approaches often apply uniform autonomy policies, ignoring user-specific expectations across different body zones.
• Significance: Ensuring perceived safety, trust, and comfort in SRLs is critical for their adoption in applications like industrial assembly, surgical assistance, and personal augmentation.
• Motivation and related work: Prior research has focused on mechanical feasibility and shared autonomy but has not addressed how SRLs should behave in intimate peripersonal spaces. Proxemics concepts have been applied to off-body robots but remain unexplored for body-mounted systems.

Solution

• Proposed approach: SRL Proxemics—a zone- and segment-level design framework for spatially calibrated, legible behaviors of SRLs in near-body interactions.
• Novelty:
  1. Introduction of a body-centric trust gradient with zone-specific autonomy and motion rules.
  2. Mixed-methods study combining user-defined elicitation and physiological measures to derive spatial policies.
  3. Empirical demonstration that autonomy preferences vary by body region and task context.
  4. Development of a three-tiered policy for zone-responsive control of SRLs.
• Procedure and key techniques:
  • Conducted a Wizard-of-Oz study with 18 participants using back-mounted SRLs.
  • Tasks included Comfort Zone and Control Handover scenarios to elicit user-defined spatial policies.
  • Compared a high-autonomy baseline with participant-defined rules (PDR).
  • Collected qualitative data (think-aloud protocols, interviews), physiological data (skin conductance responses), and subjective ratings (trust, safety, embodiment).

Results

• Concrete findings:
  • Participants segmented their bodies into zones with distinct autonomy and motion preferences: critical (e.g., face, torso), supervisory (e.g., shoulders, upper arms), and utilitarian (e.g., hands, forearms).
  • High-autonomy entries elicited higher physiological arousal (SCR peaks) than PDR entries, especially during approach/entry phases.
  • PDR increased perceived safety, trust, and embodiment compared to the high-autonomy baseline.
• Advantage over baselines:
  • PDR reduced physiological arousal during sensitive interactions and improved subjective assurance metrics (e.g., trust, safety, embodiment).
  • High-autonomy modes were perceived as less predictable and less safe, despite being more capable.
• Experiments / evaluation:
  • Mixed-methods design with 18 participants (6 female, 12 male; mean age 27.72).
  • Tasks: Comfort Zone (handover scenarios) and Control Handover (collaborative sorting).
  • Measures: qualitative spatial rules, skin conductance responses, trust and safety questionnaires, embodiment ratings.
• Limitations and future work:
  • Wizard-of-Oz setup lacks real-time autonomy and error recovery.
  • Single-session evaluation limits insights into long-term adaptation.
  • Findings are specific to back-mounted SRLs and controlled tasks; replication with diverse configurations and real-world applications is needed.
  • Proposed overlays (e.g., affect-responsive modulation) remain untested.

Summary

This paper introduces SRL Proxemics, a framework for designing spatially adaptive behaviors for supernumerary robotic limbs (SRLs) in near-body interactions. Through a Wizard-of-Oz study, participants defined zone- and component-specific autonomy rules, revealing that perceived safety and trust depend on spatially calibrated, legible behaviors rather than uniform autonomy. Participant-defined rules (PDR) reduced physiological arousal and increased subjective assurance compared to a high-autonomy baseline. The findings support a three-tiered policy for zone-responsive control and highlight the importance of user-centered design in wearable robotics. Future work should implement these policies in autonomous systems and test their applicability across diverse contexts.